1. Field of the Invention
The present invention generally relates to data communication and, in particular, to a system and method for increasing the efficiency of data communication in a cable network.
2. Related Art
The cable television industry currently transmits television signals through a cable network utilizing a combination of optical fibers and coaxial cables. This cable network is sometimes referred to as a hybrid fiber coaxial (HFC) network. In addition to the transmission of television signals, it has been recognized that the cable network can also be used to transmit other types of data between remote locations. Therefore, the cable network of the cable industry may be used as an alternative to communicating data via conventional telephone networks, such as the public switched telephone network (PSTN).
In this regard, the cable network is currently being used to transmit data to and from subscribers located at remote locations. Each subscriber location includes a cable modem capable of communicating with a controller located at a central cable station (or "head-end") that provides television signals to each subscriber modem. Cable connections between the controller at the central cable station and the subscriber modems currently exist so that movies or other types of television signals can be transmitted from the central cable station to each of the subscriber modems.
Each connection between a subscriber modem and the central cable station includes two channels, an upstream channel having one frequency range and a downstream channel having another frequency range. The upstream channel is used to transmit data from the subscriber modems to the controller at the central cable station, and the downstream channel is used to transmit data from the central cable station to the subscriber modems.
A medium access control (MAC) protocol has been devised to enable reliable communication of data across both channels of each cable connection. The MAC protocol establishes frames of information slots that are used to communicate data over the cable connections. According to one embodiment of the MAC protocol, each information slot represents a sixteen byte data packet in a data stream flowing between the central cable station and the subscriber modems via the cable connections of the cable network. Furthermore, pursuant to MAC protocol, each subscriber modem can write to the upstream channel but cannot read from it, and each subscriber modem can read from the downstream channel but cannot write to it. The MAC protocol and transmission of data via slots are well known in the art.
Since the controller at the central cable station is the only device transmitting on the downstream channel, the controller has complete access to the downstream channel. Therefore, steps do not need to be taken to ensure that data transmitted by the controller is not overwritten as a result of multiple devices trying to communicate on the same channel. However, since each of the cable modems transmit on the upstream channel, access to the upstream channel should be controlled to ensure data reliability.
To enable orderly access to the upstream channel, the controller communicates control signals to the subscriber modems via the downstream channel indicating when and what type of information each subscriber modem may communicate on the upstream channel. In this regard, the controller defines each slot within each frame on the upstream channel as either a contention slot or a data slot. The controller notifies each subscriber modem via the downstream channel of when the contention slots are present on the upstream channel such that any of the subscriber modems can write to any of the contention slots.
When a subscriber modem has data that it wishes to transmit on the upstream channel, the subscriber modem waits for the next contention slot and writes a transmission request into the contention slot when the contention slot arrives at the subscriber modem. This transmission request is transmitted by the upstream channel to the controller, which allocates a certain number of data slots to the requesting subscriber modem in response to the transmission request. The controller then informs the requesting subscriber modem when these data slots will arrive on the upstream channel so that the requesting subscriber modem may write its data into the allocated slots. The controller allocates each data slot to only one subscriber modem so that only one subscriber modem writes data to a single data slot. This prevents subscriber modems from writing over data previously written into the data slots by other subscriber modems.
A problem with the current protocol of communicating across the cable connections of a cable network is that delays exist between the time that a subscriber modem is ready to communicate data and the time that the subscriber modem is actually allowed to write data into data slots on the upstream channel. This delay is exacerbated by the fact that many transmission requests are overwritten by other subscriber modems and are, therefore, not successfully communicated to the central cable station.
In this regard, each cable modem in the cable network is allowed to write a transmission request to any of the contention slots pursuant to MAC protocol. Accordingly, when multiple cable modems write transmission requests to the same contention slot, the contention slot becomes unreadable at the central cable station. As a result, none of the transmission requests written into the contention slot are serviced by the controller at the central cable station. Therefore, each of the transmission requests written into the same contention slot is later retransmitted via another contention slot, thereby delaying the process of receiving an authorization to communicate on the upstream channel.
Thus, a heretofore unaddressed need exists in the industry for providing a system and method for reducing the delays associated with the allocation of data slots within a cable network to increase the efficiency of the cable network.